The structure of RNA is being studied by two major approaches. The first is to measure the thermodynamic parameters associated with the helix yields coil transition of synthetic model oligoribonucleotides. Thus, the contributions of helix length and sequence, mismatched bases and loops to the stability of a proposed structure can be evaluated. The goal is to accurately predict secondary structure of RNA. The second approach involves comparing the values of association constants of oligonucleotides which are complimentary to single strand portions of RNA when a well defined structural modification of the RNA is carried out. For example, when a single base is altered in a tRNA sequence, what overall changes in the structure occur? If the single base change alters the function of the tRNA, one can distinguish whether the alteration of function is a local effect involving the protein-RNA interaction, or an overall change in the secondary structure of the molecule.